Technical Abstract:
The Cullars Rotation is the oldest, continuous soil fertility experiment in the southern United States and the second oldest experiment in the world that includes cotton. It was placed on the National Register of Historical Places in 2003. It continues to document the long-term yield trends of fi ve crops in a threeyear rotation with 14 soil fertility variables. Each fertility treatment is replicated three times. On the Marvyn loamy sand where the Cullars Rotation is located, dry weather, particularly early in the growing season, limited yields of wheat, corn and cotton. Timely fall rainfall helped yields of soybean (see table). All corn and cotton plots received 120 pounds total N per acre in split applications except on plots A, B, and C. The complete fertilizer plus micronutrient treatment produced the equivalent of almost three bales of cotton per acre. In spite of the dry fall, soybean yields were generally higher than the irrigated soybean yields on the nearby Old Rotation experiment. The 2005 yields continue a trend of high yields that began about the time we converted this experiment from conventional tillage to conservation tillage in 1997. Conservation tillage includes either in-row subsoiling or paratilling prior to planting wheat, cotton, and corn. While long-term trends seem to indicate higher yields on the well-fertilized plots, the plots with low levels of one or more nutrient or factor (e.g., plot C [nothing], plot 2 [no P], plot 6 [no K], and plot 8 [no lime]), continue a trend toward lower yields. For example, plot C (nothing) produced very low yields of most crops until recently when we get nothing from this treatment. Yields on the no P, no K, and no lime plots are also decreasing.